Embodiments of the present invention relate to a sensor, gas analyzer and method for measuring a concentration of at least one respiratory gas component in a breathing gas, with varying concentration during a breathing cycle comprising an inspiration phase, an expiration phase and a phase between the inspiration and expiration.
Patients that are health monitored are usually connected to a host, such as a patient monitor. Patient monitors may include electrical cables or plastic tubing that transmit measurement samples or data from sensors attached to patient. Data and samples are usually analyzed at the host and showed on the host's display for the care giver. Cables and tubes between the patient and the host generate different problems for care givers as wired patient complicate care procedures and can create various risks for the patient. Such risks include tearing cables and tubes which may hurt and disturb the patient. While wireless sensors may decrease these problems and risks, the size, weight and operating time cause other types of problems.
To ensure good usability and functionality of breathing gas analyzers, such as a mainstream type analyzer placed close to a patient's airways into the end of the endotracheal tube, mask or prongs, it is important that the device size is small, especially with smaller patients, to ensure that the device would not prevent clinical procedures by covering critical areas of a patient's face or body. The device should also be lightweight in order to ensure that the device would not, for example, bend an endotracheal tube which could clog the air flow between the lungs and the ventilator or that the device would not unfasten from a patient's nasal or oral cavities if mask or prongs are used.
Short operating time is one of the challenges in transportable wireless gas analyzing due to the electrical power consumption of the gas analyzer. This is especially a problem with gas analyzing based on gas absorption at infrared radiation wavelengths, which is the most common and functioning real-time method in analyzing the concentration of most common gases. The most power consuming component in such an analyzer is the radiation source that generates the infrared radiation wave lengths. Optical reflector and collimator designs may increase the emitted signal efficiency few times higher, but the electrical power consumed by the radiation source still varies between approximately 1 W-1.5 W. The energy density of rechargeable lithium-ion batteries are between 150-250 Wh/l, which is one of the best, commercially available, rechargeable battery technologies at the moment. With these given values, a wireless analyzer comprising a large rechargeable battery with a size such as 100 cm3 (1 dl) would function continuously for approximately 10-25 hours. This short operating time, together with the large battery size of 100 cm3, creates a heavy analyzer and makes it difficult to treat adults and smaller patients.